Although the source example for this article relates to a twitter-controlled coffee maker, the project highlights how simple it is to control something over the Internet via twitter, an Arduino, PC and some basic circuitry. Using a Python script that allows communication between the Internet-connected PC and an Arduino board - the script searches twitter for a particular hashtag. Once that tag is found, a byte of data is sent to the Arduino board which then can take action. Here is the original project demonstration:

As the details have been published, including the Python and Arduino code, you can now have twitter help you in your remote Arduino control projects. To move forward with your own Arduino-embedded projects, consider the Freetronics LeoStick - one of the smallest Arduino-compatibles on the market with onboard USB, RGB LED and piezo: